1. Field of Invention
The invention relates to the field of cutting tools, and, in particular to reamers for use in making tapered holes.
2. Description of Prior Art
Reaming a taper requires greatly enlarging one end of the hole, with this enlargement gradually decreasing toward the other end. Thus, a tapered reamer, instead of being a finishing tool is, in reality, required to remove a considerable amount of material. Furthermore, a tapered reamer's cutting surface at the finish of the operation, is engaged throughout the entire length of the hole. Because of this, tapered reamers are subjected to much greater torsional strains than the ordinary straight reamer that cuts only on the end. The tendency, therefore, is to chatter, rifle, cut out-of-round or otherwise produce unacceptable surface finishes. Conventional tapered reamers also require high thrust and torque levels and thus have short lives. There is also a possibility of flute chipping.
A typical application for such reamers is in the preparation of holes for Taper Lok fasteners. The problems mentioned above are multiplied because, in most Taper Lok fastener applications, the hole to be reamed extends through a multiple number of parts, which may be made of different materials. Prior methods of preparing the hole required the drilling of a pilot hole, rough reaming, and fine reaming with a six fluted reamer. Quite often the hole has to be finished off with a hand reamer. Obviously, this is a time consuming and expensive procedure.
Most unacceptable surface finishes in straight or tapered holes are caused by vibrations or chatter. This problem was recognized in U.S. Pat. No. 265,998, "Reamer" by G. R. Valentine. Valentine discloses a cylindrical shank having a plurality of sets of cutting ribs equally spaced about the longitudinal axis of the shank. Each set of cutters comprises a first cutter aligned with the longitudinal axis of the shank and a second cutter at a slight angle to the longitudinal axis. These latter angled or diagonal cutter ribs alternate from right to left and from left to right. While such a configuration would probably reduce chattering in cylindrical bore, a tapered version would not have the required effectiveness when reaming tapered holes.
Accordingly, it is a general object of the present invention to provide a reamer for making tapered holes that reduces or eliminates surface imperfections.
It is another object of the present invention to provide a reamer with an extended life.
It is a further object of the present invention to provide a reamer which reduces thrust and torque load requirements of the driver.